The automated detection of rare cells in a population of different cells is a challenging problem akin to finding the proverbial needle in the haystack. Examining cell sample using traditional microscopy would require unreasonable amounts of time and is susceptible to operator error. Furthermore, in some instances, for example, the detection of microbial cells in natural water ecosystems, the characteristics of the rare cells are not already known. In such situations optical microscopy based on image processing methods is the only viable alternative. A similar approach may be needed when the cells in question are known, but they are not identifiable through any other mechanism except with traditional microscopy and image processing, e.g. in the detection of cancer cells in pap-smears.
In cases where a specific characteristic of the rare cell can be identified and located through the generation of a distinct signal, detection methods other than image processing may be employed allowing for much faster detection in a very large initial population of cells. If, for example, a cell surface antibody specific to the cell in question can be bound to a fluorescing substance, the cell can be detected using fast methods such as fluorescence activated cell sorting (FACS). In such systems though the efficiency of detection is inversely proportional to the frequency of the cells in question.
U.S. Pat. No. 4,746,179 issued on May 24, 1988 to Dahne et al. describes the use of a waveguide in conjunction with a fluorescence signal generated by the sample to estimate the concentration of a soluble antigen. Dahne et al. passes an excitation signal through the waveguide that is immersed in, or in direct contact with, the sample solution. The leakage of the excitation signal from the waveguide reacts with the solution next to the waveguide and produces a fluorescence signal that is picked up by the waveguide and directed to and measured by a detector. The strength of the fluorescence signal will be proportional to the concentration of the sample in solution.
Citation or identification of any reference in this section or any section of this application shall not be construed that such reference is available as prior art to the present invention.